The invention pertains generally to a data link controller for a local area data network. More particularly the invention relates to a data link controller that causes an acknowledgment packet to be sent without going through a separate line acquisition protocol.
As the computer using segment of the population has grown, it has become more important to share expensive assets among multiple users. For example in large companies with large mainframe CPUs, their associated peripherals, and large central data bases, as well as numerous local devices, task processors and terminals used by individual employees and subdivisions of the company, it is advantageous to have the remote users be able to share the assets of the mainframe CPU. Thus it is advantageous to have the remote task processors be able to send and receive data from the main CPU, tap the main data bases and be able to print data and store and retrieve data using the printers and magnetic storage media of the main CPU.
It is important to ascertain in each system whether the data transmitted has been received without error. To that end prior art systems have utilized acknowledgment or handshaking schemes. These acknowledgment schemes have involved preparation, by the client data processing device, of an acknowledgment packet or signal and transmission of that signal to the sending unit after going through a line acquisition protocol. The sending unit then placed the acknowledgment packet in a receive buffer which was used to store all incoming messages. Subsequently when the sending unit wanted to know whether the data packet was successfully received, it searched the receive buffer to find the acknowledgment packet corresponding to the data packet it sent.
Because the unit that wished to send an acknowledgment packet had to go through a line acquisition protocol, extra time was consumed in this process. Extra overhead time was also consumed by the sending unit in determining whether its outgoing data packet had been properly received in searching through a long receive buffer containing many messages to find the acknowledgment packet that corresponds to the data packet that was sent.
The present invention represents an improved data link controller and an improved method of transmitting and receiving data on a local area data network or other data communication network.